The role of recA protein in DNA repair and related processes is being studied. In particular, proteolytic cleavage of phage lambda repressor by recA protein is being characterized. We have isolated and mapped new mutations in the phage lambda cl gene which either enhance or inhibit in vivo induction of prophage lambda. These mutant repressors have been amplified by cloning on to plasmids and the repressors purified from the overproducing strains. We are presently characterizing the cleavage reaction between these purified mutant repressors and purified recA protein. Results to date suggest that repressor made by the phage mutant which is more sensitive to induction is cleaved more rapidly, and also aggregates to form dimers (which bind to phage operators) and higher multimers less readily than wild type repressor. These results are consistent with a model previously proposed by Dr. J.Roberts that repressor monomers, but not dimers, are substrate for recA proteolysis. In additional experiments, we have identified new regulatory mutations in the recA gene which have the properties of operator mutations. The regulatory region of recA bearing these mutations and the wild type regulatory region are being sequenced. Finally, we have shown that recA protein cleaves a cellular protein, the lexA+ gene product, but that it does not cleave lexA- mutant protein. This result is consistent with repression of the recA gene by the lexA product in uninduced cells, and with destruction of repressor by recA protein in induced cells by a mechanism similar to that for destruction of phage repressor in an induced lysogen.